Process for polymerizing a monovinyl aromatic monomer



' 3 265,766. PROCESS FOR POLYMERIZING. Ar MONO- VINYL AROMATIC MONOMER Alva F. Harris, Wilhraham, Mass.,. assignor to Monsanto Company, a corporation of Delaware No Drawing. 7 Filed June 5, 1962,. Ser; No; 200,036

12Claims. p (Cl. 260-880) I This invention relates to the polymerization of. styrenetype monomers and more particularly relates to the. use,

of a novel catalyst system in the polymerization of. such monomers. I

It is known that styrene-type monomerstcan= be polymerized thermally or catalytically toprepare polymers having molecular weights and residual monomer contents which vary with certain reaction parameters,ezg;, the catalyst concentration, the time and temperature oftthe: reaction, etc. It is also known that the-product?normallyh'as an undesirably high residual monomer content whem the parameters of. a mass pol'ymerizatiom process are con:- L

trolled so as to prepare a moldingsgrade:polystyrene,iiez,

a polystyrene having a Staudinger average molecular" weight in the range of about 40,000-100,00'0;

As shown in U.S; Patent 2,675,362, certain" catallysts sidual monomer contentswhich are occasionally en'count ered when styrene-type monomers are masspolymerized on a commercial scale.

An object of the invention is to provide a: novel process for polymerizing styrene-type monomers.

Another object is to provide a process. for polymerizin-g. styrene-type monomers inthe presence of anovel catalyst system. i a

A further object is toprovide a mass process forpolym erizing styrene-type monomers to moldable polymers con-- taining a minimum amount of residual monomer;

These and other objects are attained by (1): dissolving? acatalytic mixture of an arylethylene oxide ands a monocarboxylic acid having a dissociation constant. not higher than 1.0 at prising a monovinyl aromatic hydrocarbon and/or an:

'ar-halo monovinyl aromatic hydrocarbon and. (2) heating to polymerize the polymerizable material, the polyrrr. erization being conducted at 180-220? C. during the fin.- ishing stage of the reaction.

When desired, the catalyst mixture can 3180f include a. monomer-soluble peroxy compound having a half-life of at least 10 hours in benzene at 100 C. This optional ingredient is particularly apt to be desirable when: the invention is applied to a mass polymerization process utilizing the time-temperature cycle which is hereinafter deffined as the cycle which should be employedwhen the reaction is intended to produce a moldable polymer having a minimum residual monomer content.

' The following examples are given to illustrate the invention and are not intended as a limitation thereof. In the reactions described in these examples (1) quantities mentioned are quantities by weight unless otherwise specified, (2) the monovinyl aromatic monomers employed as starting materials are commercially-suppliecls mono content to even lower: levels United States Paten 0 f C. in a polymerizable material com-- 3,265,766 Patented August 9, 1966 mers containing 0.001-0.0015% t-butyl catechol and varying amounts of the impurities normally present in commercially-supplied styrene-type; monomers, and (3) aliquots of the same monomer sample are polymerized in any series of reactions proposed for direct comparison of results.

Example I Part A C0ntr0l: Dissolve 0.04 part of di-t-butyl peroxide-in 100. parts of styrene. Purge the reaction vessel with nitrogen and heat at- 90." C. for24 hours to convert about 32% of the styrene to polymer. Then gradually raise the reaction temperature to C. over a period of 4.75 hours and maintain the temperature at 190 C. for an additional 4 hours. The product has a Staudinger average molecular weight and a residual monomer content of 1.45%.

Parr BC0tntr0l: Repeat Part .A except for also dissolving 0.28 part of stearic acid in the monomer. The product has a Staudinger averagemolecular weight in the range of 40,000-70,000 and? a residual monomer content of 1.31%

Parr CComrol: Prepare three products by repeating Part A except for also dissolving, respectively, 0.001 part, 0.0] part, and 0.1 part of a commercial styrene oxide (99.7% pure) in the monomer. Each of the products has a Staudinger average molecular weight in the range of 40,00070,000. The residual monomer contents of the products, together-with the amounts of styrene oxide employed. in their preparation, are shown below.

Styrene Oxide Residual Reaction Number (ports) Monomer (percent) Part D: Prepare three products by repeating Part A except for also dissolving. 028 part of stearic acid and, respectively, 0001' part, 0.01 part, and'0.1 part of a commercial styrene oxide (99 .7% pure) in the monomer. Each: of. the products hasa Staudinger'average molecular weight. in the range of40,000-70,000. The residual monomer contents of theproducts, together with the amounts 8: styrene oxide. employed in their preparation, are shown low.

Styrene Oxide Residual Reaction Number (parts) Monomer 7 (percent) when Example 'I is repeated except that:

in the range of 40,000-70,000

isothermally at 90 I over a period of 4.75 hours,

(1) The time-temperature cycle employed for the reaction is (a) 24 hours at 90 C., followed by 3.5 hours at 90-185" C., followed by 1 hour at 185 C., (b) 24 hours at 90 C., followed by 6.25 hours at 90-185 C., followed by 1.5 hours at 185 C., or (c) 12 hours at l10-90 C., followed by 4.5 hours at 90-190 C., followed by 3 hours at 190 C.,

(2) The 0.001-0.1 .part of styrene oxide isreplaced with 0.001-0.1 part of o-methylstyrene oxide, p-chlorostyrene oxide, 2,5-dichlorostyrene oxide, or p-t-butylstyrene oxide,

(3) The 0.28 part of stearic acid is replaced with 0.4 part of stearic acid, 0.1 part of benzoic acid, or 0.06 part of acetic acid, or

(4) The 100 par-ts of styrene are replaced with 100 parts of p-chlorostyrene, 100 parts of a mixture of o-, m-,

and p-methylstyrenes, a mixture of 85 parts of styrene and 15 parts of acrylonitrile, a mixture of 80 parts of styrene and 20 parts of methyl methacrylate, a mixture of 75 parts of styrene and 25 parts of alpha-methylstyrene, or a solution of 10 parts of a rubbery butadienestyrene (75:25) copolymer in 100 parts of styrene.

Example II Part A-Control: Dissolve 0.04 part of di-t-butyl peroxide and 0.28 part of stearic acid in 100 parts of styrene. Purge the reaction vessel with nitrogen and heat at 90 C. for 24 hours to convert about 32% of the styrene to polymer. Then gradually raise the reaction temperature to 190 C. over a period of about 4.75 hours and maintain the temperature at 190 C. for an additional 4 hours. The product has a Staudinger average molecular weight in the range of 40,000-70,000 and a residual monomer content of 1.32%.

Part B: Prepare six products by repeating Part A except for also dissolving, respectively, 0.01 part, 0.03 part, 0.06 part, 0.1 part, 0.5 part, and 1 part ofredsitilled styrene oxide (100% pure) in the monomer. Each of the products has a Staudinger average molecular weight inthe range of 40,00070,000. The residual monomer contents of the products, together with the amounts of styrene oxide employed in their preparation, are shown below.

Styrene Oxide (parts) Residual Monomer (percent) Roactlon Number COCO Example IIL-Control Repeat Example II except for conducting the reactions C. The residual monomer contents of the products prepared in the presence of the di-t-butyl peroxide/stearic acid/styrene oxide catalyst systems are substantially the same as the residual monomer content of the product prepared in the presence of the di-t-butyl peroxide/stearic acid catalyst system.

Example IV Prepare three products by dissolving 0.28 part of stearic acid and, respectively, 0.001 part, 0.01 part, and 0.1 part of styrene oxide in 100 parts of styrene, purging the reaction vessel with nitrogen, and heating to polymerize the styrene. Maintain the reaction temperature at 90 C. for 24 hours, then gradually raise it to 190 C. and maintain it at 190 C. for an additional 4 hours. Each of the products has a Staudinger average molecular weight in the range of 40,000-70,000. The residual monomer contents of the products, together with the amounts of styrene oxide em ployed in their preparation, are shown below.

Styrene Oxide Residual Reaction Number (parts) l\lonomer (percent) wherein R is an aryl radical, e.g., phenyl, alkylphenyl, halophenyl, naphthyl, alkylnaphthyl, halonaphthyl, biphenyl, etc. Such compounds, when not easily available, can be prepared by the direct oxidation of the corresponding RCH-=CH compound with, e.g., perbenzoic acid, or by any other suitable technique. Various methods of preparing alkylene oxides are disclosed, e.g., in Migrdichian, Organic Synthesis, vol. 1, Reinhold Publishing Corporation, New York (1957), on pages 80-87.

Exemplary of utilizable arylethylene oxides are styrene oxide; ar-alkylstyrene oxides, such as o-, m-, and p-methylstyrene oxides, p-ethylstyrene oxide, p-t-butylstyrene oxide, etc.; ar-halostyrene oxides, such as o-, m-, and pchlorostyrene oxides, p-bromostyrene oxide, 2,5-dichlorostyrene oxide, 2,4 dichlorostyrene oxide, 2 chloro 4- methylstyrene oxide, etc.; ar-alkoxystyrene oxides, such as p-methoxystyrene oxide, etc.; naphthylethylene oxide; ar-substituted naphthylethylene oxides, such as the archloro and ar-methylnaphthylethylene oxides, etc., and mixtures thereof. Although, as demonstrated, these utilizable compounds can bear a plurality of ar-substituents, arylethylene oxides having ar-substituents in both of the positions ortho to the epoxyethyl group will not ordinarily be found effective in the practice of the inven ion except when they are used in conjunction with the more reactive arylethylene oxides which are free of substituents in at least one of these ortho positions. Styrene oxide is the preferred arylethylene oxide.

The reaction mixture should contain at least 0.0001% of the arylethylene oxide, based on the weight of polymerizable material, and usually contains not more than 2% of the arylethylene oxide. Concentrations lower than 0.0001% are ineffective in the practice of the invention; concentrations higher than 2% can be employed without ill effect but do not appear to offer any advantage over concentrations of l2%. Ordinarily the reaction mixture will contain 0.001-4% of the arylethylene oxide when the optional organic peroxy compound is employed as a catalyst component and 0.01-2% of the arylethylene oxide when no organic peroxy compound is employed. The weak organic acid employed as a catalyst commonocarboxylic acid having a dissociation constant not higher than l.0 10* at 25 C.

- Among the particularly suitable acids are acetic, hex'anoic,

- life of at least 10 peroxycompounds include, e.g., di-t-butyl' diperphthalate,

erizable material, and usually contains not more than. 1%

of the acid. Within the range of 0.054% and at higher concentrations, variation in the concentration of a particular acid seems to have no substantial effect on the, 'molecular weights and residual monomer contents of the polymers formed by the reaction, but it is usually preferred to avoid concentrations higher than 1% in order to avoid undue yellowing of the polymer. Ordinarily the reaction mixture will contain 0.1-0.6% of the acid.

5'-di(t-butylperoxy)hexyne-3, t-butyl hydroperoxide, cu-

mene hydroperoxide, p-menthane hydroperoxide, cyclo- -pentane hydroperoxide, diisopropyl'benzene hydroperoxide,

p-t-butylcumene hydroperoxide, pinane hydroperoxide, 2,5-dimethylhexane2,5-dihydroperoxide, etc., and mixtures thereof. i v The reaction mixture can contain up to 0.1% of the peroxy compound, based on-the weight of polymerizable material. This optional component may be found desirable when a substantial amount of the polymerization is to be accomplished at temperatures at which such peroxy compounds are effective, e.g., when the process utilizes the time-temperature cycle hereinafter defined as the cycle -to be employed in a mass process when the product is to be a moldable polymer containing a minimum amount of residual monomer. When included as a catalyst com ponent, the peroxy compound is usually employed in concentrations of 0.01-0.1%, preferably 0.01-0.05%.

The catalyst mixtures of the-invention are used in the polymerization of polymerizable materials comprising a .monovinyl aromatic hydrocarbon and/or an ar-halo monovinyl aromatic hydrocarbon, e.g.,

styrene; vinyl naphthalene; ar-alkylstyrenes, such as 0-, m-, and pmethylstyrenes, ar-ethylstyrenes, etc.; o-chlorostyrene; p-bromostyrene; 2-chloro-4-methylstyrene, etc., and mixtures thereof. Such monovinyl aromatic monomers, as is well known, normally contain minor amounts of impurities formed as by-products of the monomer synthesis or' accumulated during storage. Since the presence of these impurities appears to be more desirable than undesirable in the practice of the invention, they are not removed from the monomers prior to polymerization except when the particular application for which the product of the polymerization is intended requires the removal of one or more'particular impurities known to contribute properties which would be undesirable in that application, e.g., excessive amounts of dissolved oxygen are removed when the application will not tolerate the degree of yellowness that would be contributed to the polymer by large amounts of oxygen.

The monovinyl aromatic monomer may constitute the only component of the polymerizable material or may be in admixture with lesser amounts of one or more copolymerizable monomers, such as acrylonitrile; methacrylonitrile; an alkyl methacrylate, e.g., the methyl, ethyl, propyl, and butyl methacrylates; the corresponding alkyl acrylates; alpha-alkylstyrenes, e.g., alpha-methylstyrene, alphaethylstyrene, alpha-methyl-p-methylstyrene, etc.

When desired, the polymerizable material can have a rubbery conjugated 1,3-diene polymer (e.g., natural rubber, polybutadiene, polyisoprene, copolymers of butadiene and/ or isoprene with lesser amounts of comonomers such as styrene, acrylonitrile, methyl methacrylate, etc.) dissolved therein, ordinarily in amounts of 1-25%, based on the Weight of polymerizable material. Also, the reaction mixture can contain other optional ingredients such as plasticizers, mineral oils, stabilizers, etc.

The process of the invention is conducted at 180- 220 C., preferably 180-200 C., during the finishing stage of the reaction because of the ineffectiveness of the arylethylene oxide/weak organic acid catalyst systems at lower temperatures. Prior to the finishing stage, the reaction can be conducted under any conditions suitable to thetechnique employed (e.g., a mass, suspension, batch,

or continuous technique) and to the type of product desired. Thus, the process may be conducted at 180- 220 C throughout the reaction when a comparatively low molecular weight product is desired, whereas lower temperatures, e.g., 90 C., will be maintained for as long as is practical when a higher molecular weight product is desired. Methods of varying polymerization conditions to obtain a particular type of product are, of course,

already well known to the art. As will be readily understood, the time at which the reaction temperature should be raised to the finishing temperature will vary with the conditions which have been employed duringthe earlier stages of the reaction, sincesome of these conditions normally lead to higher degrees of conversion than others.

Ordinarily, the finishing temperature of 180-220 C. will be utilized at least during the stage of the reaction after 98% conversion of monomer to polymer.

A preferred embodiment of the invention is the use of the arylethylene oxide/weak organic acid catalyst systems in the mass polymerization of styrene-type monomers'to moldable polymers having a minimum residual In order for the product of this mass time-temperature cycle should be employed. In the first stage of the reaction, polymerization is conducted at 75-125" C. for about 6-24 hours until 15-45% of the monomer has been converted to polymer; in the second stage, the reaction temperature is gradually raised from 75-95 C. to l80-200 C. over a period of about 3-7 hours; in the final stage, the reaction temperature is maintained at ISO-200 C. for about 0.5-5 hours.

The manner of manipulating the reaction temperature 5 during the first stage of the reaction in order to be in the 75-95 C. range for the beginning of the second stage of the reaction is-not critical, e.g., an initial temperature of about 100-125 C. can be gradually lowered to 75-95 C.

1 during the first stage of the reaction or the temperature can be maintained at -95 C. throughout the first stage of the reaction, etc. According to a particularly preferred embodiment of the invention, the reaction mixture is initially heated to -115" C. and maintained at a temperature gradually lowered to about 90 C. until about 25-45% conversion to polymer is obtained, after which the temperature is gradually raised to -200 C. over a period of about 3-7 hours and then maintained at 180- 200 C. for about 2-5 hours to complete the reaction.

Especially good results are also obtained by initially heating the reaction mixture at 90 C. to about 25-35% conversion, then heating at a temperature gradually raised to 180-200 C. over a period of about 4-5 hours, and finally heating at ISO-200 C. for 2-4 hours.

Although also generally useful as a new catalytic meth- 0d of polymerizing styrene-type monomers, the present invention is particularly advantageous in that it permits the formation by a mass process of moldable polystyrenetype materials having lower residual monomer contents than the comparable polymers of the prior art. The reduced residual monomer content improves the physical and molding properties of the polymers. 3

It is obvious that many variations can be made in the products and processes set forth abovewithout departing from the spirit and scope of this invention.

What is claimed is:

l. A process which comprises (1) dissolving a catalyst pound having a half-life zene at 100 C.

of at least 10 hours in benpolymerizable material comprising a monovinyl aroma-tic monomer of the group consisting of a monovinyl aromatic hydrocarbon, an ar-halo monovinyl aromatic hydrocarbon, and mixtures thereof, and (2) heating to polymerize a substantial percentage of the polymerizable material at a temperature below 180 C.; and 3) heating the partially polymerized material at a temperature of 180-220 C. during the finishing stage of the polymerization reaction.

2. A mass polymerization process which comprises (1) dissolving a catalyst mixture consisting of:

(a) at least 0.0001 part by weight of an arylethylene oxide, (b) 0.05-1 part by weight of a monocarboxylic acid having a dissociation constant not higher than at.25 C., and about 0.01 to 0.1 part by weight of a peroxy compound having a half-life of at least hours in benzene at 100 C.

in 100 parts by weight of a polymen'zable material comprising a monovinyl aromatic monomer of the group consisting of a monovinyl aromatic hydrocarbon, an ar-halo 7. The process material contains polymer.

of claim 2 wherein the polymerizable a dissolved rubbery conjugated 1,3-diene 8. The process of claim 2 wherein the arylethylem oxide is styreneoxide.

9. The process of claim 2 acid is an alkanoic acid cont 10. The process of claim ture consists of (a) 0.01-2 ethylene oxide and b) 0.1 carboxylic acid having a than 1.0 10- at 25 C.

11. The process of claim 2 ture consists of (a) 0.001-1 part by weight of an arylethylene oxide, (b) 0.1-0.6 part by weight of a monocarboxylic acid having a dissociation constant not higher than 1.O 10- at 25 C., and (c) 0.01-0.1 part by weight of a peroxy compound having a half-life of at least 10 hours in benzene at C.

12. A mass pblymerization (l) dissolving a catalyst mixture consisting of (a) 0.001-

wherein the monocarboxylir aining 12-20 carbon atoms 2 wherein the catalyst mixparts by weight of an aryl- -0.6 part by weight of a monodissociation constant not higher wherein the catalyst mix- References Cited by the Examiner UNITED STATES PATENTS,

2,521,754 9/1950 Shusman 260-935 2,534,120 12/1950 Glick 26093.5 2,675,362 4/1954 Shusman 260-935 2,839,490 6/1958 Grotz et a1.

260-867 FOREIGN PATENTS 1,088,230 9/1960 Germany.

JOSEPH L. SCHOFER, Primary Examiner.: JAMES A. SEIDLECK, Examiner. J. M. DULIN, Assistant Examiner. 

2. A MASS POLYMERIZATION PROCESS WITH COMPRISES (1) DISSOLVING A CATALYST MIXTURE CONSISTING OF: (A) AT LEAST 0.001 PART BY WEIGHT OF AN ARYLETHYLENE OXIDE, (B) 0.05-1 PART BY WEIGHT OF A MONOCARBOXYLIC ACID HAVING A DISSOCIATION CONSTANT NOY HIGHER THAN 1.0X10-4 AT 25*C., AND (C) ABOUT 0.01 TO 0.1 PART BY WEIGHT OF A PEROXY COMPOUND HAVING A HALF-LIFE OF AT LEAST 10 HOURS IN BENZENE AT 100*C. IN 100 PART BY WEIGHT OF A POLYMERIZABLE MATERIAL COMPRISING A MONOVINYL AROMATIC MONOMER OF THE GROUP CONSISTING OF A MONOVINYL AROMATIC HYDROCARBON, AN AR-HALO MONOVINYL AROMATIC HYDROCARBON, AND MIXTURES THEREOF (2) HEATING THE POLYMERIZABLE MATERIAL AT 75-125*C. UNIT 15-45% CONVERSION TO POLYMER IS OBTAINED, THE TEMPERATURE BEING SO REGULATED AS TO BE IN THE 75-95*C. RANG WHEN THIS CONVERSION IS OBTAINED, (3) GRADUALLY RAISING THE REACTION TEMPERATURE TO 180-200*C. OVER A PERIOD OF ABOUT 3-7 HOURS, AND (4) MAINTAINING THE REACTION TEMPERATURE AT 180-200*C. FOR ABOUT 0.5-5 HOURS
 7. THE PROCESS OF CLAIM 2 WHEREIN THE POLYMERIZABLE MATERIAL CONTAINS A DISSOLVED RUBBERY CONJUGATED 1,3-DIENE POLYMER. 